In a conventional image forming apparatus, a toner image can be fixed at a low temperature and a heating roller included in a fixing device is thin while a warm-up time is shortened and a power consumption is reduced. A toner having a glass transition temperature TG of 50 degrees centigrade or less is used to form the toner image that can be fixed at a low temperature. In such an image forming apparatus, a temperature at which high temperature offset of the toner occurs is low, and heat conduction in an axial direction of the heating roller deteriorates. Therefore, if sheets are continuously longitudinally fed, a temperature of a portion where no sheet passes at both ends of the heating roller rises, thereby facilitating occurrence of an overheated state. If the toner image is fixed in such a state, the high temperature offset may occur in the portion where no sheet passes, resulting in a fixing failure. There is a problem that the high temperature offset in the portion where no sheet passes conspicuously easily occurs when the toner capable of being fixed at a low temperature is used; however, the high temperature offset also occurs when other toners are used.